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3D object snaps allow you to specify points on 3D objects that regular object snaps won’t recognize — for example, the center of a face, or a vertex. You enable 3D object snaps by clicking the 3D Object Snap button on the status bar. Right-click the 3D Object Snap button and choose the running 3D object snap modes you want to use.

Object snap tracking allows you to calculate points that are not on an object by using object snap points on existing objects. When working in 3D, you can not only track points on the current X, Y plane but also along the Z axis.

While tracking points along the Z axis, AutoCAD provides feedback in the form of a tooltip that lets you know you’re moving along the Z axis in the positive or negative direction.

The ELEVATION system variable allows you to specify a height above or below the current working plane. When you enter a 2D coordinate, AutoCAD uses the value assigned to ELEVATION system variable (by default, it’s 0) to create a 3D coordinate. You can set the OSNAPZ system variable to 1, to

substitute the Z coordinate value of a point specified by using an object snap with the value of ELEVATION.

Changing Planes

Come fly with us while we explain changing planes in AutoCAD. (Just step through this metal detector over here while we X-ray your bags.)

Okay, it’s not that kind of plane. This section covers using the user coordinate system (UCS) to control the current working (or X, Y) plane. The UCS icon displayed either at the lower-left corner of the drawing window or at the origin (0, 0, 0) shows you the orientation of the current work plane and the positive direction of the Z axis.

Displaying the UCS icon

By default, the UCS icon is displayed in both 2D and 3D views. You can lose your bearings pretty easily when working in 3D, and we strongly recommend that you keep the UCS icon in your sights at all times. If you don’t see a UCS icon, you can turn it on from the Coordinates panel of the View tab on the Ribbon. Click the button with the burned-out light bulb and choose either Show UCS Icon or Show UCS Icon at Origin.

In addition to controlling the display of the UCS icon, you can also tweak its size, color, and location by using the UCS Icon dialog box. To display the UCS Icon dialog box, choose UCS Icon, Properties on the Coordinates panel of the Home tab.

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480 Part V: On a 3D Spree

In previous releases, the UCS icon was merely a graphic indicator of the current coordinate system. If you set a new user coordinate system in model space, the UCS icon adjusted itself to show you the orientation of the new X, Y plane and Z axis. In other words, the UCS icon was driven by the current coordinate system. Beginning with AutoCAD 2012, the UCS icon moves across to the driver’s seat! You can now select the UCS icon and see new multifunction grips that allow you to set a new UCS by dragging the grips on the origin and the legs of the icon. There’s also a new right-click menu. You can enable or disable UCS icon selectability on the Settings tab of the UCS dialog box — type UCSMAN to open it. In the next section, we show you how to create a new user coordinate system by selecting and manipulating the UCS icon.

Adjusting the UCS

Every drawing you create uses the World Coordinate System (WCS), but when working in 3D, you need to create additional work planes. User coordinate systems (UCSs) are necessary when you need to draw objects on work planes other than the WCS. In the real world, think of latitude and longitude as the WCS; street naming, house numbering, and hotel room numbers are all local systems and are equivalent to UCSs. Traditional UCSs are static; create one, and it stays current until you change it. By default, such coordinate systems are unnamed, but you can assign a name and save it for future use. A couple of releases back, AutoCAD introduced dynamic UCSs. Because dynamic is the opposite of static, what you get is a temporary coordinate system that changes as you move your mouse pointer over different planar faces of a 3D object. Use the status bar Allow/Disallow Dynamic UCS button on the status bar, or press the F6 key to toggle dynamic UCS on and off.

Name that UCS

The UCS command offers ten options to help you define a new UCS. Access the UCS command options from the Coordinates panels on either the View or Home tab of the Ribbon.

The most commonly used options of the UCS command are listed below. After you select one of these options from the Ribbon, follow the command prompts at the command line or the Dynamic Input prompt.

World: Align the UCS to match the WCS.

Face: Align the UCS to the face of a 3D solid.

View: Align the UCS so that the X plane is perpendicular to your current viewing direction.

3 Point: Specify a new origin for the UCS, and then the positive direction of the X and Y axes. Alternatively, use the multifunction grips on AutoCAD’s UCS icon to create a new UCS by moving and realigning the icon.

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For more information on all the UCS command’s options, refer to AutoCAD’s online help system.

The more UCSs in your drawing, the more you need help managing them. AutoCAD offers a handy dandy UCS dialog box for doing just that. Open it by clicking the dialog box launcher (the little arrow at the right end of the panel label) on the Coordinates panel of the View or Home tab, or simply type UCSMAN and press Enter. The three tabs in the UCS dialog box are

Named UCSs: Lists World and other user coordinate systems. Set a UCS current with the Set Current button, or right-click a UCS to rename or delete a named UCS. (You can’t rename or delete the World UCS.)

Orthographic UCSs: Lists the six default orthographic coordinate systems (front and back, left and right, top and bottom) relative to the WCS. These UCSs are automatically created by AutoCAD and can’t be deleted or renamed.

Settings: Controls properties of both the UCS icon and the UCS itself.

After you define a UCS that you think you might want to use again, you can save it in the UCS dialog box. We explain how in the following steps, which you begin by creating a solid box.

1.Start a new 3D drawing by selecting acad3d.dwt (or acadiso3d. dwt for the metric crowd) for your template, and ensure that the 3D Modeling workspace is current.

Refer to the steps in the “Entering the third dimension” section, earlier in the chapter, if you need a refresher.

2.On the Modeling panel of the Home tab, click Box.

AutoCAD prompts:

Specify first corner or [Center]:

3. Type 0,0,0 and then press Enter.

AutoCAD anchors the first corner of the box at the origin of the WCS and prompts:

Specify other corner or [Cube/Length]:

4.Drag your crosshairs away from the first corner and click a point to set the length and width of the box.

Exact distances don’t matter in this example. AutoCAD prompts:

Specify height or [2Point]:

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482 Part V: On a 3D Spree

5.Drag the crosshairs upward from the second corner and click to set the height of the box.

AutoCAD creates the 3D box and exits the command. Preliminaries are over. Now it’s time to start making some UCSs.

6.Move the crosshairs over the UCS icon.

The UCS icon shows the orientation of the World Coordinate System. As you move the crosshairs over the icon, it turns a greenish-gold color, indicating that it can be selected.

7.Click to select the UCS icon.

A square multifunction grip appears at the origin, and round multifunction grips appear at the ends of the icon’s legs.

8.Move the crosshairs over each multifunction grip and look at the grip menus.

Hovering over one of the round grips at the end of a leg lets you choose between realigning the selected axis, or rotating the UCS around one of the unselected axes. Hovering the mouse pointer over the origin grip lets you move the UCS origin to a new location and either keep the current alignment of the X and Y axes or realign them. The third grip option, World, restores the WCS.

Now you use the UCS icon’s multifunction grips to set a new UCS.

9.Click the UCS icon to select it, and then move the crosshairs over the square multifunction grip at the origin.

The crosshairs jump to the origin and the grip menu appears.

10.From the grip menu, choose Move and Align.

AutoCAD prompts:

** MOVE AND ALIGN **

Specify origin point or align to face, surface, or mesh:

Move the crosshairs to a different corner of the box, and when the UCS icon origin is over the corner, click to set the new origin.

If you want, you can drag the round grips on the axes to realign the new UCS. After you have it the way you want, it’s worth saving it. The next steps show how.

11.On the Coordinates panel of the Home tab, choose UCS, Named UCS.

AutoCAD displays the UCS dialog box.

12.With the Named UCSs tab current, select Unnamed in the UCSs list.

The new, unnamed UCS is the current UCS in the drawing and is listed at the top of the list.

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Chapter 21: It’s a 3D World After All 483

13.Right-click Unnamed and choose Rename from the shortcut menu.

An in-place editor is displayed that allows you to rename the UCS.

14.Type a name for the new UCS press Enter.

The Unnamed UCS is renamed (see Figure 21-3).

Figure 21-3: Naming a custom UCS.

15.Click OK.

The UCS dialog box closes, and the new UCS is saved in the drawing.

16.On the Coordinates panel of the Home tab, choose UCS, World.

The current UCS is now aligned with the WCS.

17.On the Coordinates panel of the Home tab, click in the Named UCS drop-down list and choose the name of the UCS you just saved.

The new UCS is restored.

AutoCAD likes giving you lots of choices. You can also restore a named UCS from the UCS drop-down list at the bottom of the ViewCube. (We fill you in on the ViewCube in the “Taking a spin around the cube” section, later in this chapter.) Or you can right-click the UCS icon, choose Named UCS, and then choose the UCS from the menu.

Using Dynamic UCS

A named UCS allows you to work on different work planes, but it can take a bit of effort to set up and that can distract you when you’re focused on 3D modeling. With Dynamic UCS, you can focus on modeling, not on creating a UCS. To enable or disable the dynamic UCS feature, click the Dynamic UCS button on the status bar.

Figure 21-4 shows an example of drawing a circle on the side of a 3D solid. With Dynamic UCS enabled, AutoCAD highlights the face of the 3D solid that

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